The Embryonic Stem Cell Core will provide expertise and services related to production of differentiated cardiac myocytes from cultured embryonic stem cells. The cells provided will be for the design of experiments to perform the proposed structure-function studies of cardiac myocyte membrane and myofibrillar proteins. The services provided will be the growth, transfection, section and differentiation of embryonic stem (ES) cells in vitro. ES cells will be used as a means for examining the phenotypes of gene knock-outs or expression of mutant proteins on either a null or wild-type background. ES cells are a necessary method to analyze cardiac phenotypes in knock-outs that are prenatal lethals in vivo. ES cells also permit screening of mutant phenotypes before investing the time and funds to generate transgenic mice that express mutant proteins.